Empty indicator for raw coal pipes and the like



15, 1956 L. M. KEEPHART 2,745,920

EMPTY INDICATOR FOR RAW COAL. PI PES AND THE! LIKE Filed June 18, 19513m entor LESTER M. KEEPHART u l ttorneg United States Patent EMPTYINDICATOR FOR RAW COAL PIPES AND THE LIKE Lester M. Keephart, Chester,Pa. Application June 18, 1951, Serial No. 232,083 3 Claims. (Cl.200-61.21)

This invention relates to means for giving an alarm or signal when thecoal or like loose material in a socalled raw coal pipe falls below agiven level therein.

In large coal burning power plants the coal customarily is fed bygravity from a hopper into the top of the pipe and conducted by thelatter to a ball mill or other pulverizing apparatus which reduces it tofinely divided condition; it is then picked up by a current of highpressure air supplied by a blower and carried to the point at which itis burned. Not infrequently, however, the mass of coal in the hopperforms an arch over the hopper outlet to the pipe and so prevents thecoal from feeding normally into the latter. As a consequence after allthe coal in the pipe at the time the arch forms has passed into the millthe high pressure air can enter the pipe from below in a blast ladenwith dense clouds of coal dust which, escaping through seams in the pipeand other confining walls into the plant before the blower can be shutoff, contaminate the atmosphere, soil objects on which the dust thensettles, and sometimes create fire and explosion hazards.

Raw coal pipes in installations of the character to which reference hasbeen made extend vertically from the elevated hopper to the pulverizingmill and are sometimes eighty feet or more in length and sixteen inchesor thereabouts in diameter, the pipe itself thus constituting a coalreservoir of considerable volume; the mill and associated mechanism maytherefore continue to be supplied with coal therefrom for some littletime after an arch has been formed in the hopper over the upper end ofthe pipe and prevented passage of coal thereinto. Such arches cannotreadily be located by inspection, however, and it has heretofore beendifiicult to prevent the wide dispersion of coal dust resulting fromtemporary failure of the coal supply in the manner described despite thefact that when known to exist such arches can usually quickly bedestroyed merely by vibrating the pipe and/ or hopper with a few blowsfrom a sledge hammer or in other relatively simple manner and the saideffects of the stoppage of coal feed from the hopper into the top of thepipe thus obviated.

It is therefore a principal object of my invention to provide automaticmeans for supplying a signal to indicate normal coal feed through theraw coal pipe has been interrupted with consequent necessity forappropriate action to restore the feed before the residual coal in thepipe is exhausted, although it will of course be evident the inventionis useful in other generally similar situations.

A further object is the provision of means responsive to the level ofloose material in a vertical or substantially vertical pipe or conduitwhich are maintained inoperative by the material itself when thequantity in the pipe is at or above a predetermined level but whichfunction to actuate a visual or other suitable signal when the saidmaterial falls below that level and are returned to inoperativecondition upon restoration thereof.

Other objects, purposes and advantags of the invention will hereafterappear or be understood from the following description of a preferredembodiment of it as somewhat diagrammatically illustrated in theaccompanying drawing showing partly in elevation and partly in verticalaxial section a portion of a raw coal pipe with the said embodiment ofthe invention incorporated therein.

Referring now more particularly to the drawing the pipe P may representany substantially vertical conduit for material such as coal to be fedby gravity downwardly therethrough, and in accordance with the inventionat a convenient point in the wall of the pipe there is provided anaperture 1 at a height such that between it and the lower end of thepipe there will be a reservoir of considerable capacity. The edge of thepipe wall defining the lower edge of the aperture is preferably beveledoppositely inward to form a knife-edge 3 for supporting an invertedsubstantially V-shaped actuating lever 4 for oscillatory movementrelatively to the pipe, a felt or other resilient seal 5 occupying thespace between the lever and the upper edge of the aperture to assist inkeeping the latter relatively impermeable to the escape of coal dust orair although permitting limited movement of the lever; within the pipeabove aperture 1 a fixed angularly projecting baffle or shield 6 tendsto exclude the solid material in the pipe from contact with seal 5. Onthe outer surface of the pipe is secured a housing 7 enclosing the outerarm of the lever, a compression spring 8 interposed between saidouter'arm and the housing wall urging the lever counterclockwise in thedrawing and a self-closing switch 1% adapted to be held open by thelever arm when the latter is swung outward against the bias of spring 8.Leads 11, 12 connect switch 10 in circuit with a source of current (notshown) and a lamp 13 or other indicating or alarm device which may belocated at any convenient point at which an alarm signal readily may bereceived by the operative responsible for restoring normal coal feedfollowing interruption thereof. In the side of housing 7 there isthreaded a test screw 15 which may be operated when desired to move theouter arm of the lever inward and thus allow switch 10 to close to testthe operability of the system.

When normal feed conditions obtain lever 4 is held by the pressure ofthe coal or other material in the pipe and against the spring bias insuch position as to maintain the switch and hence the circuit throughlamp 13 open, the lever offering no appreciable obstruction to thepassage of the coal vertically downward through the pipe, and theseconditions persist so long as the latter remains filled at least to thelevel of the lever whether or not the coal is actually feeding throughthe pipe.

Upon the formation of an arch in the hopper over the inlet to the pipeor occurrence of some other condition preventing passage of coalthereinto the level of the coal in the pipe gradually falls due towithdrawal from its lower end and as this level recedes below lever 4spring 8 actuates the latter in a counterclockwise direction in thedrawing, thereby allowing switch 10 to close and thus energize the alarmcircuit to afford visual or audible indication of interruption of feedand inform operatives that suitable measures must be taken to correctthe situation before substantial exhaustion of the residual material inthe pipe below the lever and ensuing admission of high pressure air tothe pipe. Of course as soon as the arch is broken or other feedinterrupting condition remedied additional coal passes into the pipeuntil it is again substantially filled and as the coal level rises abovelever 4 the latter is again swung outward to the position, as shown,which it occupies under normal conditions, with consequent interruptionof the alarm circuit and cessation of the alarm.

As has been mentioned, lever 4 and associated mechanism should belocated far enough above the bottom of the pipe so the alarm will begiven while there is still sufficient residual coal in the pipe tomaintain the teed to the pulverizing apparatus for a time adequate topermit the breaking of the arch in the hopper or, in lieu thereof, theshutting ofi of the blower before substantiaily all the coal iswithdrawn; the minimum distance above the bottom of the pipe at whichthe lever is disposed will therefore usually primarily be determined bythe rate of feed from the pipe.

It now will be apparent that my invention solves in a simple andefiicient Way an annoying, troublesome and even dangerous problem in theoperation of coal feeding and other installations of the characterdescribed and further that the apparatus utilized is of non-complicateddesign and is not liable to get out of order or become damaged under theconditions of use to which it is necessarily subjected, while it may bereadily installed in either existing installations or in new ones at arelatively low cost. I have herein described one embodiment of theinvention with considerable particularity as applied to an installationof specific character but it will be understood 1 do not desire orintend thereby to limit or confine myself in any way as changes andmodifications in the form, structure, arrangement and mode of operationof the several parts will readily occur to those skilled in the art andmay be made if desired without departing from the spirit and scope ofthe invention as defined in the appended claims;

Having thus described my invention, I claim and desire to protect byLetters Patent of the United States:

1. In apparatus affording a signal when the height of a column of loosematerial falls below a predetermined level, a pipe enclosing thematerial and having an aper ture in its wall defined in part by asubstantially horizontal knife edge, an inverted generally f-shapedlever supported on said edge for oscillation relatively to the pipe, theinner arm of the lever extending into and the outer arm extendingexteriorly of the pipe, a resilient seal interposed between the leverand the upper edge of the aperture, an electric switch adapted foractuation by the outer arm of the lever, and a spring biasing said outerarm toward the pipe whereby when the level of the material in the pipeis above said inner arm and its pressure thereagainst exceeds the biasof the spring said outer arm is held in switch actuating position.

2. In apparatus affording a signal when the height of a column of loosematerial falls below a predetermined level, a pipe enclosing thematerial and having an aperture in its wall defined in part by asubstantially horizontal knife edge, an inverted generally V-shapedlever supported on said edge for oscillation relatively to the pipe, theinner arm of the lever extending into and the outer arm extendingexteriorly of the pipe, an electric switch adapted for actuation by theouter arm of the lever, and a spring biasing said outer arm toward thepipe whereby when the level of the material in the pipe is above saidinner arm and its pressure thereagainst exceeds the bias of the springsaid outer arm is held in switch actuating position.

3. In apparatus afiording a signal when the height of a column of loosematerial falls below a predetermined level, a pipe enclosing thematerial and having an aperture in its wall defined in part by asubstantially horizontal knife edge, an inverted generally V-shapedlever supported on said edge for oscillation relatively to the pipe, theinner arm of the lever extending into and the outer arm extendingexteriorly of the pipe, a spring biasing said outer arm toward the pipe,said inner arm being adapted for limited movement toward said wallagainst the bias of the spring when engaged by said material, and aswitch cooperative with the outer arm of the lever to make and break anelectric circuit upon oscillation of said lever.

References Cited in the file of this patent UNITED STATES PATENTS848,519 Versteeg Mar. 26, 1907 1,847,844 McLaren Mar. 1, 1932 1,885,051Smulski Oct. 25, 1932 1,892,790 Smelser Jan. 3, 1933 2,043,530 DezotellJune 9, 1936 2,349,519 Reichenstein May 23, 1944 2,611,044 Siemon Sept.16, 1952 2,615,102 McMath Oct. 21, 1952 FOREIGN PATENTS 414,117 GermanyMay 23, 1925 540,295 Great Britain Oct. 13, 1941

